Type annotations for `util.data`. (#18963)
Summary:
I haven't had a chance to rigorously try these out yet so don't merge yet.
Closes #18725.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18963
Differential Revision: D14832897
Pulled By: ezyang
fbshipit-source-id: 4780e7a34126bc66ddbfd9d808dfc9e0edd77e68
